Circuit breakers are commonly used for providing automatic circuit interruption upon detection of undesired overcurrent conditions on the circuit being monitored. These overcurrent conditions include, among others, overload conditions, ground faults and short-circuit conditions.
Circuit breakers typically include an electrical contact on a movable arm which rotates away from a stationary contact in order to interrupt the current path. In response to an overcurrent condition, circuit breakers generally move the arm to break the current path by tripping a spring-biased latch mechanism. The latch mechanism includes a bearing surface for supporting a cradle which, in turn, is coupled to the movable arm. Tripping the latch mechanism causes the bearing surface to release the cradle, thereby forcing the arm and its contact away from the fixed contact.
A drawback of some existing latch mechanisms is that the bearing surface of the latch mechanism may fail to release the cradle in response to the latch mechanism being tripped, thereby preventing interruption of the current path during an overcurrent condition. Also, the bearing surface of the latch mechanism may improperly release the cradle without being tripped so as to interrupt the current path during normal operating conditions. In an effort overcome this drawback and achieve proper operation of the latch mechanism, the bearing surface may be lubricated or buffed. This solution, however, is unsatisfactory because it results in relatively large manufacturing tolerances and because it increases the cost of production due to the addition of a separate process step for lubrication or buffing.
Accordingly, there is a need for a latch mechanism for a circuit breaker which overcomes the above-mentioned deficiencies of the prior art.